A method of manufacturing a fine pattern includes a photo lithography method, an ion beam method, a laser exposure method and the like. Here, since line width of an ion beam is narrow, a fine pattern having a further fine line width can be fabricated, and thus the ion beam method is used to manufacture a cutting-edge product or a semiconductor of high integrity. The laser exposure method forms the fine pattern through an etching process by irradiating a laser beam after coating a substrate with a photosensitive film whose properties are changed by the laser beam.
However, although such a laser exposure method may fabricate a fine pattern in a speedy way, the line width in the plane direction is thick compared with that of the ion beam method, and thus the width of the fine pattern is limited. In addition to the line width in the plane direction, it is difficult to control depth of exposure (i.e., depth of the photosensitive film whose properties are changed when the laser is irradiated on the photosensitive film) or to finely set a value of the depth of exposure.
In a conventional technique, in order to reduce the depth of exposure (hereinafter, referred to as a height direction line width), a lot of studies for reducing the plane direction line width of the laser beam have been conducted since the height direction line width is proportional to the plane direction line width of the laser beam around the focus. However, such a plane direction line width is limited due to diffraction limit of an exposure lens. Here, the plane direction line width according to the diffraction limit is defined by mathematical expression 1 shown below.
                              2          ⁢                                          ⁢                      W            0                          =                              1.22            ⁢            λ                    NA                                    [                  Mathematical          ⁢                                          ⁢          expression          ⁢                                          ⁢          1                ]            
Here, denotes a wavelength of a laser beam, 2W0 denotes a plane direction line width around the focus, and NA denotes the number of apertures of an exposure lens (diameter of exposure lens/focal distance). Accordingly, due to the diffraction limit, the size of the plane direction line width is limited depending on the wavelength of the laser. Furthermore, in the case where the photosensitive film is formed as multiple layers, although only the photosensitive film positioned on the top layer needs to be exposed, undesired photosensitive films are deformed if the height direction line width is not controlled, and thus it is worried that defective products are mass produced. Particularly, the height direction line width needs to be finely fabricated recently in order to manufacture and use laminated semiconductors.
FIG. 1 is a side view mimetically showing a laser beam 10 passing through an exposure lens 110 and irradiated on a photosensitive film 6 having triple layers in a conventional technique. FIG. 2 is an enlarged view showing the laser beam 1 around the focus, passing through the exposure lens 110 of FIG. 1 in the conventional technique. In addition, FIG. 3 is an enlarged view showing the laser beam 1 around the photosensitive film 6, passing through the exposure lens 110 of FIG. 1 in the conventional technique, and FIG. 4 is a graph showing a relation between height direction (Z-axis direction) and intensity of laser beam, from which exposure depth formed by a conventional fine pattern manufacturing apparatus can be figured out.
As shown in FIGS. 1 to 4, in the case of a fine pattern manufacturing apparatus according to a conventional laser exposure method, height direction line width H is larger than a desired exposure depth, and thus defective products are mass produced. Since such a height direction line width H is defined by mathematical expression 2 shown below, the height direction lien width H is also limited by the wavelength of a laser beam like the plane direction line width 2W0.
                    H        =                              2            ⁢            π            ⁢                                                  ⁢                          W              0              2                                λ                                    [                  Mathematical          ⁢                                          ⁢          expression          ⁢                                          ⁢          2                ]            
Accordingly, required is a laser exposure method, in which an interference laser beam having an interference fringe direction is formed in the height direction, and the resolution of height direction can be improved by controlling line width of height direction to be reduced.